Linear Dependence of Photoluminescence in Mixed Ln-MOFs for Color Tunability and Barcode Application

Portable, Intelligent Fluorescence Sensing Platform for Dense Convolutional Network-Capable Detection of Indophenol Sulfate and Methylmalonic Acid Using a Luminescent Eu@HOF Film

Indophenol sulfate (IS) and methylmalonic acid (MMA) are biomarkers of chronic kidney disease (CKD) and diabetes polyneuropathy (DPN), respectively. Portable and accurate monitoring of IS and MMA is very important to ensuring human health. The dense convolutional network (DenseNet) with image recognition has great potential in fluorescence sensing, but developing a platform with high precision and portability to diagnose the disease still faces huge challenges. Herein, we developed a high-sensitivity platform with a fluorescence material, a smartphone, and the DenseNet to monitor IS and MMA. A red-emitting Eu@PFC-13 (1) is prepared, and 1 shows high selectivity and low detection limits (DLs) to detect IS and MMA. The sensing mechanism of 1 toward IS and MMA is investigated by experiments and theoretical calculation. For detecting IS and MMA in serum and urine, 1 is fabricated into an Eu@PFC-13/AG (2) film with DLs of 1.4 and 1.6 μM, respectively. In addition, a portable smartphone platform is designed to monitor IS and MMA with high precision. Moreover, the DenseNet is constructed by Python, which can output the concentration of analytes by identifying fluorescence images and judge whether any is in a dangerous range. This work not only proposes a novel method that integrates a fluorescence material, a smartphone, and deep learning to detect analytes but also opens a new way for the diagnosis of CKD and DPN.

Metal Doping to Control Gate Opening and Increase Methane Working Capacity in Isostructural Flexible Diamondoid Networks

Adsorbed natural gas (ANG) systems involve using porous materials to increase the working capacity and/or reduce the storage pressure compared to compressed natural gas (CNG). Flexible metal-organic materials (FMOMs) are particularly interesting in this context since their stepped isotherms can afford increased working capacity if the adsorption/desorption steps occur within the proper pressure range. We report herein that metal doping in a family of isostructural FMOMs, ML₂ (M=Co, Ni or Ni_x Co_1-x , L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), enables control over the gate opening between non-porous (closed) and porous (open) phases at pressures relevant to methane storage. Specifically, methane-induced phase transformations can be fine-tuned by using different Ni/Co ratios to enhance methane working capacity. The optimal working capacity from 5 to 35 bar at 298 K (153 cm³  cm^-3 ) was found for Ni_0.89 Co_0.11 L₂ (X-dia-1-Ni_0.89 Co_0.11 ), which is greater than that of benchmark rigid MOFs.

Dynamic Anti-Counterfeiting Labels with Enhanced Multi-Level Information Encryption

Information encryption is an important means to improve the security of anti-counterfeiting labels. At present, it is still challenging to realize an anti-counterfeiting label with multi-function, high security factor, low production cost, and easy detection and identification. Herein, using inkjet and screen printing technology, we construct a multi-dimensional and multi-level dynamic optical anti-counterfeiting label based on instantaneously luminescent quantum dots and long afterglow phosphor, whose color and luminous intensity varied in response to time. Self-assembled quantum dot patterns with intrinsic fingerprint information endow the label with physical unclonable functions (PUFs), and the information encryption level of the label is significantly improved in view of the information variation in the temporal dimension. Furthermore, the convolutional residual neural networks are used to decode the massive information of PUFs, enabling fast and accurate identification of the anti-counterfeit labels.

Turn-up Luminescent Sensing of Ultraviolet Radiation by Lanthanide Metal-Organic Frameworks

Here, we report a series of two-dimensional lanthanide metal-organic frameworks Ln-DBTPA (where DBTPA = 2,5-dibromoterephthalic acid and Ln = Tb (1), Eu (2), or Gd (3)) showing a unique turn-up responsiveness toward ultraviolet (UV) radiation. The luminescence enhancement was derived from the accumulated radicals that can promote the intersystem crossing process. The compound 1 shows an ultralow detection limit of 9.1 × 10^-9 J toward UV radiation, representing a new type of luminescent UV detectors.

Recent advances in luminescent metal-organic frameworks and their photonic applications

In recent years, metal-organic frameworks (MOFs) have been attracting ever more interest owing to their fascinating structures and widespread applications. Among the optoelectronic materials, luminescent MOFs (LMOFs) have become one of the most attractive candidates in the fields of optics and photonics thanks to the unique characteristics of their frameworks. Luminescence from MOFs can originate from either the frameworks, mainly including organic linkers and metal ions, or the encapsulated guests, such as dyes, perovskites, and carbon dots. Here, we systematically review the recent progress in LMOFs, with an emphasis on the relationships between their structures and emission behaviour. On this basis, we comprehensively discuss the research progress and applications of multicolour emission from homogeneous and heterogeneous structures, host-guest hybrid lasers, and pure MOF lasers based on optically excited LMOFs in the field of micro/nanophotonics. We also highlight recent developments in other types of luminescence, such as electroluminescence and chemiluminescence, from LMOFs. Future perspectives and challenges for LMOFs are provided to give an outlook of this emerging field. We anticipate that this article will promote the development of MOF-based functional materials with desired performance towards robust optoelectronic applications.

Laterally Engineering Lanthanide-MOFs Epitaxial Heterostructures for Spatially Resolved Planar 2D Photonic Barcoding

Metal-organic frameworks (MOFs) heterostructures with domain-controlled emissive colors have shown great potential for achieving high-throughput sensing, anti-counterfeit and information security. Here, a strategy based on steric-hindrance effect is proposed to construct lateral lanthanide-MOFs (Ln-MOFs) epitaxial heterostructures, where the channel-directed guest molecules are introduced to rebalance in-plane and out-of-plane growth rates of the Ln-MOFs microrods and eventually generate lateral MOF epitaxial heterostructures with controllable aspect ratios. A library of lateral Ln-MOFs heterostructures are acquired through a stepwise epitaxial growth procedure, from which rational modulation of each domain with specific lanthanide doping species allows for definition of photonic barcodes in a two-dimensional (2D) domain with remarkably enlarged encoding capacity. The results provide molecular-level insight into the use of modulators in governing crystallite morphology for spatially assembling multifunctional heterostructures.

Achieving colour tuneable and white-light luminescence in a large family of dual-emission lanthanide coordination polymers

Expanding the family of lanthanide terpyridine coordination polymers has yielded eighteen new complexes with two different phases, Ln(TPC)₂(HCOO)(H₂O) (Ln-1) and Ln(TPC)(HCOO)₂ (Ln-2) (Ln = Sm-Lu, except Tm). Both structures are composed of lanthanide cations interconnected by 2,2':6',2''-terpyridine-4'-carboxylate ligands to yield one-dimensional chain topologies. However, the incorporation of an additional crystallographically unique decorative TPC ligand into Ln-1 gives rises to a distinct phase. The encapsulation of both metal- and ligand-based phosphors within single coordination polymers leads to dual-emission of the afforded materials. Furthermore, judicious lanthanide doping in heterometallic Ln-1 and Ln-2 allows for fine-tuning the photoluminescent colours over a wide range of gamut. Such a combination showcases the capability to fine-tune the emission colours from deep green, to red, and to blue. In addition, direct white-light emission upon UV excitation can be achieved in the Sm_xGd_1-x-1 system.

Theoretical hydrogen bonding calculations and proton conduction for Eu(iii)-based metal-organic framework

A water-mediated proton-conducting Eu(iii)-MOF has been synthesized, which provides a stable proton transport channel that was confirmed by theoretical calculation. The investigation of proton conduction shows that the conductivity of Eu(iii)-MOF obtained at 353 K and 98% RH is 3.5 × 10-3 S cm-1, comparable to most of the Ln(iii)-MOF based proton conductors.

Recent progresses in luminescent metal-organic frameworks (LMOFs) as sensors for the detection of anions and cations in aqueous solution

The discharge of excessive metal ions and anions into water bodies leads to the serious pollution of water and environment, which in turn has a certain impact on industry, agriculture, and human life. Because of the unique advantages of luminescent metal-organic frameworks (LMOFs), they have been successfully explored as various fluorescent probes to quickly and effectively detect these pollutants. This perspective not only introduces the design strategy and classification of LMOFs, especially the construction methods of water-stable LMOFs, but also reports the latest progresses in some LMOFs between 2016 and 2020 as well as expounds the mechanisms of LMOFs for detecting anions and cations. Moreover, the luminescence properties of LMOFs are related to the selection of metal ions, the structure of organic ligands, the pore size, and the interaction of guest molecules. Finally, the further development of LMOFs is summarized and prospected in this field.

Tuning of the Network Dimensionality and Photoluminescent Properties in Homo- and Heteroleptic Lanthanide Coordination Polymers

Targeted synthesis, through a heteroleptic methodology, has resulted in three types of lanthanide (Ln) coordination polymers (CPs) with tailored dimensionality, tunable photoluminescent colors, and distinct luminescence quenching upon UV and X-ray irradiation. The homoleptic Ln(tpbz)(NO₃)₂ [CP-1; tpbz = 4-(2,2':6',2″-terpyridin-4'-yl)benzoate] is assembled from Ln cations and bridging tpbz ligands, accompanied by the decoration of NO₃^- anions, forming a one-dimensional (1D) chain structure. The presence of ancillary dicarboxylate linkers, 1,4-benzenedicarboxylate (bdc) and 2,5-thiophenedicarboxylate (tdc), promotes additional bridging between 1D chains to form a two-dimensional layer and a three-dimensional framework for Ln(tpbz)(bdc) (CP-2) and Ln(tpbz)(tdc) (CP-3), respectively. The multicolor and luminescence properties of the obtained CPs were investigated, displaying typical red Eu^III-based and green Tb^III-based emissions. The Sm^III-bearing CP-1-CP-3, however, exhibit diverse ratiometric Ln^III- and ligand-based emissions, with the photoluminescent colors varying from pink to orange to cyan. Notably, the Tb^III-containing CP-1-CP-3 display distinct luminescence quenching upon continuous exposure to UV and X-ray irradiation. To our best knowledge, CP-2-Tb represents one of the most sensitive UV dosage probes (3.2 × 10^-7 J) among all CPs.

Luminescence tuning and sensing properties of stable 2D lanthanide metal–organic frameworks built with symmetrical flexible tricarboxylic acid ligands containing ether oxygen bonds

New Ln-MOFs were yielded by a flexible ligand and lanthanide ions. The colors can be regulated by adjusting the molar ratios of Eu³⁺/Tb³⁺, showing promising applications in NB sensing, tunable photoluminescence and pH sensing.

Four anionic Ln-MOFs for remarkable separation of C2H2–CH4/CO2–CH4 and highly sensitive sensing of nitrobenzene

Ln-MOFs with open metal active sites and Lewis basic nitrogen atoms show highly sensitive sensing of nitrobenzene and remarkable separations of C₂H₂–CH₄/CO₂–CH₄.

An ultralight charged MOF as fluoro-switchable monitor for assorted organo-toxins: size-exclusive dye scrubbing and anticounterfeiting applications via Tb3+ sensitization

The trifunctional Li(i)-MOF acts as fluoro-switchable sensor for two organo-toxins, invisible-ink based data encrypter and size–specific dye scavenger, where DFT calculations support sensing and adsorption mechanisms considering extended structure.

A trimeric tri-Tb3+ including antimonotungstate and its Eu3+/Tb3+/Dy3+/Gd3+-codoped species with luminescence properties

A trimeric tri-Tb3+-including antimonotungstate (AMT) hybrid Na17{(WO4)[Tb(H2O)(Ac)(B-α-SbW9O31(OH)2)]3}·50H2O (Tb3W28) was successfully synthesized, in which the capped tetrahedral {WO4} group plays a significant template role in directing the aggregation of three [B-α-SbW9O33]9- fragments and three Tb3+ ions. Eu3+/Tb3+/Dy3+/Gd3+-codoped AMT materials based on Tb3W28 were firstly prepared and their luminescence properties were investigated. The red emitter Eu3+, yellow emitter Dy3+, and nonluminous Gd3+ ions were codoped into Tb3W28 to substitute Tb3+ ions for investigating the energy transfer (ET) mechanism among Eu3+, Tb3+, and Dy3+ ions. Upon the 6H15/2 → 4I13/2 excitation at 389 nm of the Dy3+ ion, the ET1 mechanism (Dy3+ → Tb3+) was confirmed as a non-radiative dipole-dipole interaction. Under the 7F6 → 5L10 excitation at 370 nm of the Tb3+ ion, the ET2 mechanism (Tb3+ → Eu3+) was identified as a non-radiative quadrupole-quadrupole interaction. Under excitation at 389 nm, the two-step successive Dy3+ → Tb3+ → Eu3+ ET3 process was proved in Dy1.2Tb3zEu0.03Gd1.77-3zW28. Through changing the excitation wavelengths, the emission color of Dy1.2Tb1.2Eu0.03Gd0.57W28 can vary from blue to yellow, in which a near-white-light emission case was observed upon excitation at 378 nm. This work not only provides a systematic ET mechanism study of hetero-Ln-codoped AMTs, but also offers some useful guidance for designing novel performance-oriented Ln-codoped polyoxometalate-based materials.

Faithful Fabrication of Biocompatible Multicompartmental Memomicrospheres for Digitally Color-Tunable Barcoding

Barcodes have attracted widespread attention, especially for the multiplexed bioassays and anti-counterfeiting used toward medical and biomedical applications. An enabling gas-shearing approach is presented for generating 10-faced microspherical barcodes with precise control over the properties of each compartment. As such, the color of each compartment could be programmatically adjusted in the 10-faced memomicrospheres by using pregel solutions containing different combinations of fluorescent nanoparticles. During the process, three primary colors (red, green, and blue) are adopted to obtain up to seven merged fluorescent colors for constituting a large amount of coding as well as a magnetic compartment, capable of effective and robust high-throughput information-storage. More importantly, by using the biocompatible sodium alginate to construct the multicolor microspherical barcodes, the proposed technology is likely to advance the fields of food and pharmaceutics anti-counterfeiting. These remarkable properties point to the potential value of gas-shearing in engineering microspherical barcodes for biomedical applications in the future.

Terbium-based metal-organic frameworks: highly selective and fast respond sensor for styrene detection and construction of molecular logic gate

Volatile organic compounds (VOCs) are extremely harmful to the human body and environment, thus it is greatly meaningful and urgent to detect VOCs. In this work, terbium-based metal-organic frameworks (Tb-MOFs) have been prepared successfully via a facile and efficient route. These well-constructed Tb-MOFs architectures exhibit characteristic green emission of Tb³⁺ ion upon excitation of UV light. It is noteworthy that the Tb-MOFs can act as a convenient and efficient luminescent sensor for VOCs. Especially, the Tb-MOFs displayed high selectivity and superior sensitivity towards the sensing of styrene solution and vapor through fluorescence quenching mechanism. The Tb-MOFs can realize fast detection for styrene vapor with a response time of 30 s. The mechanism of fluorescence quenching of Tb-MOFs induced by styrene was also discussed. More importantly, we have designed a logic gate operation with the combination of the sensor for the intelligent detection of styrene. This developed type of lanthanide luminescent metal-organic frameworks (Ln-MOFs) based on the combination of fluorescence sensor and logic gate has a great application prospect in the detection of VOCs in daily life.

Preparations, Structures and Luminescence Properties of Penta-rare-earth Incorporated Tetravacant Dawson Selenotungstates and Their Ho3+ /Tm3+ Co-doped Derivatives

A family of penta-rare-earth incorporated tetravacant Dawson selenotungstates [H₂ N(CH₃ )₂ ]₁₀ H₃ [SeO₄ RE₅ (H₂ O)₇ (Se₂ W₁₄ O₅₂ )₂ ] ⋅ 40H₂ O [RE=Ho³⁺ (1), Er³⁺ (2), Tm³⁺ (3), Tb³⁺ (4)] were synthesized. It should be noted that a penta-RE [SeO₄ RE₅ (H₂ O)₇ ]¹¹⁺ central core connecting two tetra-vacant Dawson-type [Se₂ W₁₄ O₅₂ ]^12- subunits generates a dimeric assembly of [SeO₄ RE₅ (H₂ O)₇ (Se₂ W₁₄ O₅₂ )₂ ]^13- in the structures of 1-4. Meanwhile, a class of Ho³⁺ /Tm³⁺ co-doped derivatives based on 1 with a Ho³⁺ /Tm³⁺ molar ratio of 0.75:0.25-0.25:0.75 were also prepared and characterized by energy-dispersive spectroscopy (EDS) analyses. Moreover, their luminescence properties were systematically investigated, which indicate that Tm³⁺ ions can sensitize the emission of Ho³⁺ ions in the visible region and prolong the fluorescence lifetime of Ho³⁺ ions to some extent. Energy transfer from Tm³⁺ ions to Ho³⁺ ions was probed by time-resolved emission spectroscopy (TRES), and the CIE 1931 diagram has been applied to evaluate all possible luminescence colors.

Dual-Mode Photonic Sensor Array for Detecting and Discriminating Hydrazine and Aliphatic Amines

Colorimetric chemosensors have attracted tremendous interest for sensing hazardous substances in an uncomplicated and economical manner. Herein, a series of push-pull dicyanovinyl-substituted oligothiophene derivatives were designed, and the impacts of different end-cappers on their photophysical properties were comprehensively investigated. Interestingly, combined with a zinc porphyrin derivative (Zn-TPP), one dicyanovinyl-substituted oligothiophene derivative (NA-3T-CN) can be further developed into colorimetric and fluorescent sensor array for dual-mode detection of aliphatic amines and hydrazine. The obtained sensors showed satisfactory results between optical response and analyte's concentration both in selective single-sensor type and in enhanced multisensory mode. Based on the fluorescence change of the NA-3T-CN system, the detection limit for N₂H₄ was calculated to be around 1.22 × 10^-5 mol/L in THF. The stained TLC-supported sensor array offers obvious optical changes for down to 0.5 wt % hydrazine solution for naked-eye sensing. An aromatic amine like aniline has no obvious effect on the dicyanovinyl-substituted oligothiophene derivatives. We also found that a zinc porphyrin derivative has an obvious colorimetric response to the presence of hydrazine, ethanolamine, and aniline. Furthermore, smartphone-enabled readout system and data treatment based on RGB changes of the sensor array were performed, and the discrimination capability among hydrazine, aliphatic amines, and aromatic amine was satisfactory. In this regard, related push-pull oligothiophene derivatives not only can be regarded as models for a fundamental understanding of the relationship between molecular structure and photophysical properties but also present potential applications in the field of real-time and visual detection of hazardous chemicals.

A new photochromic Gd-MOF with photoswitchable bluish-white to greenish-yellow emission based on electron transfer

A new Gd-MOF exhibits interesting properties of photoswitchable bluish white light to greenish yellow light emission as a result of electron transfer (ET). Photoluminescence studies on the dual-emitter Gd-MOF, which paves the way for white emission though ET.

Upconversion Nanoparticles@Carbon Dots@Meso-SiO2 Sandwiched Core-Shell Nanohybrids with Tunable Dual-Mode Luminescence for 3D Anti-Counterfeiting Barcodes

Development of advanced fluorescent materials for constructing a secure and unclonable encryption is urgently required; however, their application in anti-counterfeiting applications is a great challenge. In this work, we proposed and synthesized a new type of upconversion nanoparticles@carbon dots@meso-SiO₂ nanohybrids by integrating two fluorescent materials of lanthanide-doped NaYF₄ upconversion nanoparticles (UCNPs) and carbon dots (CDs) into mesoporous silica (mSiO₂) to produce a novel sandwichlike core-shell structure and a dual-mode fluorescence from UCNPs and CDs. By tailoring the UCNP core of different upconversion luminescence, all three kinds of dual-mode luminescent UCNPs@CDs@mSiO₂ nanohybrids exhibited typical RGB upconversion luminescence under a 980 nm laser and blue downconversion luminescence under a 365 nm UV light. Due to strong the hydrophilic nature of the nanohybrids, they can be further fabricated into environmentally benign luminescent inks for creating highly secured, fluorescent-based, three-dimensional anti-counterfeiting barcodes via inkjet printing. The resultant UCNPs@CDs@mSiO₂ inks with a dual-mode and tunable luminescence nature endow the inkjet-printing barcodes with an extremely high encoding capacity and high security. Such dual-mode fluorescent inks and barcodes are simple to fabricate, easy to view, efficient for coding, and difficult to clone, thus making them promising nanomaterials for anti-counterfeiting applications.

Photoluminescent organisms: how to make fungi glow through biointegration with lanthanide metal-organic frameworks

We show that filamentous fungi can emit green or red light after the accumulation of particulate lanthanide metal-organic frameworks over the cell wall. These new biohybrids present photoluminescence properties that are unaffected by the components of the cell wall. In addition, the fungal cells internalise lanthanide metal-organic framework particles, storing them into organelles, thereby making these materials promising for applications in living imaging studies.

Influence of counter ions on structure, morphology, thermal stability of lanthanide complexes containing dipicolinic acid ligand

Two kinds of lanthanide coordination polymers formed by dipicolinic acid with lanthanide ions were synthesized by varying the counter ions. And their crystal structures, morphology and thermal stabilities were measured and compared. X-ray single-crystal diffraction analysis reveals that Na₃[Ln(DPA)₃] (Ln = Tb or Eu) stretches to a rigid network by means of bridging Na⁺ ion. Moreover, Na₃[Ln(DPA)]₃ exhibits good thermal stability and luminescent properties, and its optical properties can be remained even after heating at 200 °C more than 3 days. However, when Na⁺ in Na₃[Ln(DPA)₃] was replaced with NH₄⁺, i.e., (NH₄)₃[Ln(DPA)₃] with a supramolecular structure based on π-π stacking and other weak interactions, shows relatively poor thermal stability which leads to deterioration of their luminescence properties after heating treatment. This result confirms that the rigid frame structure of Na₃[Ln(DPA)]₃ plays a crucial role in improving its thermal stability and keeping its highly luminescent quantum efficiency.

Tunable Light Emission and Multiresponsive Luminescent Sensitivities in Aqueous Solutions of Two Series of Lanthanide Metal-Organic Frameworks Based on Structurally Related Ligands

Two series of lanthanide metal-organic frameworks (Ln-MOFs) from two structurally related flexible carboxylate-based ligands were solvothermally synthesized. H₃L2 with additional -CH₂- group provides more flexibility and different coordination modes and conformations compared with H₃L1. As a result, 2-Ln MOFs are modulated from two-dimensional kgd of 1-Ln to three-dimensional rtl topological frameworks and further achieve enhanced chemical stability. The Eu- and Tb-MOFs exhibit strong fluorescent emission at the solid state because of the antenna effect of the ligands. Interestingly, the emissions can be tuned by simply doping Eu³⁺ and Tb³⁺ of different concentrations within the Eu _xTb_{1- x} MOFs. Notably, 2-Ln MOFs realize nearly white light emission by means of a trichromatic approach (red of Eu(III), green of Tb(III), and blue of the H₃L2 ligand). Furthermore, 2-Ln MOFs also exhibit water stability and demonstrate high selective and sensitive sensing activities toward Fe(III) and Cr(VI) in aqueous solutions. The results further highlight the importance of the ligand flexibility on tuning MOF structures with improved structural stability and ion-sensing properties.

Selective Adsorption of Water, Methanol, and Ethanol by Naphthalene Diimide-Based Coordination Polymers with Constructed Open Cu2+ Metal Sites and Separation of Ethanol/Acetonitrile

The selective separation of ethanol/acetonitrile by porous materials has rarely been observed owing to their similar physicochemical properties. In this work, we report a new coordination network, [Cu₂(4-pmntd)₂(opd)₂](4-pmntd = N,N'-bis(4-pyridymethy)naphthalene diimide, opd = disodium 1,2-benzenedicarboxylate), which exhibits selective separation of ethanol over acetonitrile. The weak coordination bonds formed by unsaturated Cu²⁺ sites and hydroxyl groups are the key to such performance.

A quantitative transmetalation with a metal organic framework compound in a solid–liquid interface reaction: synthesis, structure, kinetics, spectroscopy and electrochemistry

A Zn(ii)-MOF (1) can be transformed to its isomorphous Cu(ii)-MOF (2) quantitatively in a single crystal to single crystal metal exchange process in a solid–liquid interface reaction.

Doubly interpenetrated indium-tricarboxylate frameworks mediated by small molecules with enhanced porosity

A synthetic strategy of indium-tricarboxylate frameworks by using small molecule regulators has been proposed to obtain four types of In-based coordination polymers with doubly interpenetrated structures.

Lanthanide-Based Coordination Polymers With 1,4-Carboxyphenylboronic Ligand: Multiemissive Compounds for Multisensitive Luminescent Thermometric Probes

Reactions in water of lanthanide chlorides with the sodium salt of 1,4-carboxyphenylboronic acid lead to two series of isostructural compounds with respective general chemical formulas [Ln(cpb)₃(H₂O)₂]_∞ for Ln = La or Ce and [Ln(cpbOH)(H₂O)₂·(cpb)]_∞ for Ln = Pr-Lu (except Pm) plus Y. Heterolanthanide coordination polymers that are isostructural to the second series have been synthesized, and their photophysical properties have been studied. This study evidences that it is possible to design multiemissive lanthanide-based coordination polymers that could find their application as multigauge luminescent thermometric probes.

A series of 3D lanthanide coordination polymers decorated with a rigid 3,5-pyridinedicarboxylic acid linker: syntheses, structural diversity, DFT study, Hirshfeld surface analysis, luminescence and magnetic properties

Single crystal X-ray diffraction studies reveal the formation of six new coordination polymers (CPs) with the general formulas [Dy(3,5-pdc)(3,5-pdcH)(H2O)2]n·nH2O (1), [Pr2(3,5-pdc)3(H2O)2]n·2n(H2O) (2), [Sm2(3,5-pdc)3(H2O)3]n·nH2O (3), {[Eu2(3,5-pdc)3(H2O)3(CH3CHO)]n·n[2(H2O)(DMF)]} (4), {[Gd2(3,5-pdc)3 (H2O)2]n·2nH2O} (5) and [Er(3,5-pdc)(adip)0.5(H2O)]n (6) (where 3,5-pdc2- = fully deprotonated; 3,5-pdcH- = partially deprotonated 3,5-pyridinedicarboxylic acid; adip2- = fully deprotonated adipic acid; and DMF = dimethylformamide) by solvothermal self-assembly of lanthanide ions with rigid 3,5-pyridinedicarboxylic acid as a linker and adipic acid as an auxiliary flexible spacer (only coordinated in CP 6). CPs 1 and 2 crystallize in the triclinic P1[combining macron] space group, whereas CPs 3, 4 and 6 crystallize in the monoclinic P21/n, P21/c and C2/c space groups, respectively. CP 5 exhibits the trigonal R3 space group. The 3,5-pdc ligand exhibits eight diverse coordination modes in CPs 1-6, whereas the adipic acid spacer in CP 6 shows only one coordination mode (μ4-κO:κO,O:κO:κO,O). The organic ligands interconnect with metal ions to generate 3D metal-organic frameworks with a variety of intriguing topologies. Theoretical studies, DFT calculations and Hirshfeld surface analysis support the structures adopted by the various CPs. CPs 3 (Sm) and 4 (Eu) emit strong ligand-sensitized characteristic f-f luminescence. Weak ferromagnetic interactions have been studied at low temperatures for CP 1 and CP 5.